Use lazy Workhorse upload preauth for fallback routes

This changes upload preauthorization on fallback routes from eager and optimistic (Workhorse assumes the upload is authorized and buffers the file to disk) to lazy (Workhorse queries an internal API endpoint when it encounters an upload). This only applies to MIME multipart uploads. Explicit Workhorse upload routes (such as CI artifacts) are not affected by this change.

Closes gitlab-com/gl-infra/scalability#1756 (closed).

Part of gitlab-com/gl-infra&742 (closed). Previously: !88167 (merged), !89256 (merged).